This invention relates to a process for the dehydrogenation of gaseous hydrocarbons and the catalyst employed. More specifically the process is a cyclic process wherein there are alternating cycles of dehydrogenation and catalyst regeneration.
The process is a cyclic process in which gaseous hydrocarbons such as butane, isopentane or ethylbenzene are dehydrogenated over a suitable catalyst to produce butenes and butadiene, isopentene and isoprene and styrene, respectively. After each dehydrogenation cycle there is a catalyst regeneration cycle in which the accumulated coke is burned off by passing molecular oxygen through the catalyst followed by another dehydrogenation cycle and so on.
The chromia-alumina catalysts have been recognized for a number of years as the most preferred catalysts for this type of process. The chromia-alumina catalysts are prepared by treating activated alumina with a solution of chromic acid, draining off the excess acid from the alumina, drying and heat treating at about 1400.degree.F. Commercial chromia-alumina dehydrogenation catalysts normally contain about 20% chromium oxide. Preparative methods are shown, for example, in U.S. Pat. Nos. 2,399,678 and 2,419,997.
Other chromia-metal oxide materials have been investigated for their dehydrogenation capabilities. One of the more prominent among these has been chromia-magnesia which has been found to be a poor second to chromia-alumina. Several patents were issued to Tropsch in the late 1930's relating to magnesia based chromia dehydrogenation catalysts, e.g., U.S. Pat. Nos. 2,122,786; 2,122,787; 2,122,790; and 2,148,140. Pitzer disclosed chromia-magnesiaalumina dehydrogenation catalyst in U.S. Pat. No. 2,638,455. U.S. Pat. No. 3,781,376, discloses magnesium chromites promoted with aluminum.
It is a principal feature of the present invention that improved magnesium chromite catalysts have been developed. It is another feature of the present invention to find a catalyst superior to the chromia-alumina catalysts for use in dehydrogenation. It is still an advantage that a process which will give better results than presently achieved with chromia-alumina catalysts has been provided. Other features and advantages of the present invention will be apparent from the following description.